Known glazing structures or laminates employ a layer of PVB (Polyvinylbutyral) between, for example, two glass sheets. Such known laminates are produced by passing two heated glass sheets with the PVB therebetween through nip rollers and into an autoclave.
When there is a requirement to laminate glass sheets, particularly toughened glass sheets, which incorporate apertures or holes which are subsequently employed for locating attachment means to secure the laminate, several problems arise as follows:
(a) The need to use thick PVB to handle distortion and bow associated with use of rollers in forming toughened glass and to avoid entrapped air bubbles.
(b) The PVB melts around the holes and is subsequently difficult to clear.
(c) It is difficult to place inserts, e.g. attachment nuts, in the laminate.
(d) The glass sheets tend to move in relation to each other as they pass through the nip rollers making alignment of holes in adjacent glass sheets extremely difficult to achieve.
It has been found that some of these problems can be reduced by using known so-called cast-in-place laminating techniques.
The cast-in-place technique involves making a thin glass cell, filling with a suitable liquid resin material and curing that resin to form a laminate. This is achieved by applying a peripheral seal around the edge of one glass sheet which also acts as a spacer and placing the second glass sheet over the first to produce a cell and pouring liquid resin between the two glass sheets. The edge seal is typically butyl or foam tape.
The space is filled usually from the top while the glass sheets are held at an angle and the hydrostatic pressure pushes the glass sheets apart making them bow outwardly slightly, thus more liquid, normally about 15%, can be poured between the glasses to allow for shrinkage during the curing stage.
During this filling process the edges of the glass sheets are clamped to prevent them from separating under the hydrostatic pressure and to prevent liquid resin escape at the edges of the glass sheets.
When the required volume of liquid resin has been poured into the cell, the cell is brought into the horizontal so that all the air between the glass sheets is forced out and the air space totally filled with the liquid resin. The resin is then cured by, for example, exothermic catalytic reaction or UV initiated means. The unsightly edge seal can be cut off if the glass sheets are annealed.
However, to laminate glass sheets, particularly those of the toughened type, incorporating apertures or holes using the cast-in-place technique, a major difficulty encountered is to prevent liquid resin loss from the space between the glass sheets in the region around the apertures or holes during the liquid resin filling and curing stages.